Popular recipes tagged "introspection" but not "type"

Unit Testing Nested Functions (Python)

2016-11-10T10:23:11-08:00

Python recipe 580716 by Alfe (introspection, nested, unittests). Revision 3.

Python allows the declaration of nested functions. These are typically hard to unit test because using just the normal ways of calling they cannot be called from outside their surrounding function. So they cannot be considered a clearly separated unit and thus cannot be unit tested.

This is a drawback of using them, so many developers (especially the ones deep into test driven development who strive to have a high unit test coverage) tend to avoid them in favor for standalone functions which can be called from the unit tests without any hassle.

But not all solutions with nested functions can be written as elegant with standalone functions. Nested functions are powerful insofar that they can access the local variables of the surrounding function without any need to pass them into the nested function, thus the code can in many cases stay neat and tidy while using a standalone function instead might raise the need to pass the complete context in form of a bunch of parameters. Also, using nested functions makes their local usage clear to any reader and keeps the name space tight.

But at least in the standard CPython (i. e. not necessarily in Jython, etc.) the implementation of functions (and methods) allows to find the nested function's code, wrap it properly to give it its needed context and then call it from the outside. I wrote a small module which helps doing exactly this.

Show OS error codes and messages from the os.errno module (Python)

2017-03-01T17:18:23-08:00

Python recipe 580759 by Vasudev Ram (commandline, introspection, libraries, python, unix, utilities, windows).

This recipe is a simple Python introspection utility that displays the defined OS error codes and messages (that Python knows about) from the os.errno module. It works for both Python 2 and Python 3. For each kind of OS error defined in Python, it will display a serial number, the error code, and the corresponding error name, and English error message. E.g. the first few lines of its output are shown below:

$ py -2 os_errno_info.py

Showing error codes and names

from the os.errno module:

Python sys.version: 2.7.12

Number of error codes: 86

Idx Code Name Message

0 1 EPERM Operation not permitted

1 2 ENOENT No such file or directory

2 3 ESRCH No such process

3 4 EINTR Interrupted function call

4 5 EIO Input/output error

More information, full output and other details are available here:

https://jugad2.blogspot.in/2017/03/show-error-numbers-and-codes-from.html

Find the arity of a Python function (Python)

2017-01-30T14:09:47-08:00

Python recipe 580753 by Vasudev Ram (functions, introspection, python, python2, reflection).

This recipe shows how to find the arity of a given Python function. The arity of a function is the number of arguments the function takes. The recipe uses the inspect module of Python.

More details and sample output (including some limitations) here:

https://jugad2.blogspot.in/2017/01/finding-arity-of-python-function.html

Two quick functions for object introspection (Python)

2017-01-14T22:35:17-08:00

Python recipe 580747 by Vasudev Ram (attributes, debugging, functions, introspection, methods, objects, reflection).

This recipe shows two quick-and-clean :) utility functions for introspection of Python objects. They are meant to be used while working interactively in the reular Python shell or in the IPython shell. Both of them display attributes of any given object passed as the argument. The first function displays all attributes. The second function only displays atttributes that do not begin and end with a double underscore, so as to filter out "dunder" methods a.k.a. "special" methods - like __len__, __str__, __repr__, etc. The first function - oa(o) , where o is some object - does the same as dir(o), but is useful - in IPython - because, dir(o) output will scroll off the screen if the output is long, since it prints the attributes vertically, one per line, while oa(o) prints them horizontally, so has less chance of the output scrolling off, and the output also occupies fewer lines on the screen, so is easier to scan quickly. The second function - oar(o) - is like oa(o), but filters out attribute names that begin and end with a dunder. So it is useful in both IPython and Python.

More information and outputs here:

https://jugad2.blogspot.in/2017/01/two-simple-python-object-introspection.html

How a Python function can find the name of its caller (Python)

2015-09-30T15:12:17-07:00

Python recipe 579105 by Vasudev Ram (evaluation, introspection, python, sys).

This recipe shows how a Python function can find out the name of its caller, i.e. which other Python function has called it.

Name a lambda (Python)

2014-07-02T20:54:01-07:00

Python recipe 578902 by David Weil (func_name, introspection, lambda, name, naming).

A very simple recipe to allow you easily name lambda-objects (or other kind of objects, callable, for example, partial objects) you create, with little overhead and friendly syntax.